The present invention relates to a pellet former for use with an annular gap extruder or expander.
A recent development in the feed industry has been the use of extruder type high compression screws to highly condition animal feeds prior to pelleting. Feed material is subjected to a high degree of mechanical shear and heat in the extruder, softening the feed material. The material is then expanded and formed through pelletizing discs.
Current practice generally requires the transport of this softened, expanded feed material to a separate pelleting system. Typically, conveyors and surge bins are utilized in the feed transport system. Such extruder, feed transport and pelleting systems require large amounts of floor space. Additionally, the feed material cools and becomes less soft before it is processed by the pelleting system. As a result, higher mechanical forces are required to make the pellets.
U.S. Pat. No. 5,242,292, discloses an extruder with a pelleting head adjacent the outlet end of the extruder barrel. A rotatable, multiple-vane plate pushes unexpanded material deposited in the pelleting head through a pellet die. The plate may be coupled to the primary extruder screw or secured to a separate primary mover. The device of U.S. Pat. No. 5,242,292 utilizes a cooling water jacket to control the temperature of the material as it passes through the extruder. Such temperature maintenance is designed to prevent expansion of the material as it emerges from the pelleting head. Expansion of the material as it exits the die results in less dense pellets. The pellets produced by this apparatus must be dried from a moisture level of 18-30% to 8-14% by weight.